let _chalk, _oldColor

export default async (newColor, oldColor = '#409EFF') => {
  if (typeof newColor !== 'string') return
  // 将颜色值改变成可能出现的值的数组
  const id = 'chalk-style'
  const getThemeCluster = (theme) => {
    const tintColor = (color, tint) => {
      let red = parseInt(color.slice(0, 2), 16)
      let green = parseInt(color.slice(2, 4), 16)
      let blue = parseInt(color.slice(4, 6), 16)

      if (tint === 0) {
        // when primary color is in its rgb space
        return [red, green, blue].join(',')
      } else {
        red += Math.round(tint * (255 - red))
        green += Math.round(tint * (255 - green))
        blue += Math.round(tint * (255 - blue))

        red = red.toString(16)
        green = green.toString(16)
        blue = blue.toString(16)

        return `#${red}${green}${blue}`
      }
    }
    const shadeColor = (color, shade) => {
      let red = parseInt(color.slice(0, 2), 16)
      let green = parseInt(color.slice(2, 4), 16)
      let blue = parseInt(color.slice(4, 6), 16)

      red = Math.round((1 - shade) * red)
      green = Math.round((1 - shade) * green)
      blue = Math.round((1 - shade) * blue)

      red = red.toString(16)
      green = green.toString(16)
      blue = blue.toString(16)

      return `#${red}${green}${blue}`
    }
    const clusters = [theme]
    for (let i = 0; i <= 9; i++) {
      clusters.push(tintColor(theme, Number((i / 10).toFixed(2))))
    }
    clusters.push(shadeColor(theme, 0.1))
    return clusters
  }
  const updateStyle = (style, oldCluster, newCluster) => {
    let newStyle = style
    oldCluster.forEach((color, index) => {
      newStyle = newStyle.replace(new RegExp(color, 'ig'), newCluster[index])
    })
    return newStyle
  }
  const getCSSString = (url) => {
    return new Promise((resolve) => {
      const xhr = new XMLHttpRequest()
      xhr.onreadystatechange = () => {
        if (xhr.readyState === 4 && xhr.status === 200) {
          _chalk = xhr.responseText.replace(/@font-face{[^}]+}/, '')
          resolve(true)
        }
      }
      xhr.open('GET', url)
      xhr.send()
    })
  }
  // 将旧的值和新的值都替换下
  const themeCluster = getThemeCluster(newColor.replace('#', ''))
  // 如果全局_oldColor没有值，则
  if (!_oldColor) {
    _oldColor = getThemeCluster(oldColor.replace('#', ''))
  }

  // 如果第一次转变主题颜色则...
  if (!_chalk) {
    const version = require('element-ui/package.json').version
    const url = `https://unpkg.com/element-ui@${version}/lib/theme-chalk/index.css`
    await getCSSString(url)
  }

  const newStyle = updateStyle(
    _chalk,
    _oldColor,
    themeCluster
  )

  let styleTag = document.getElementById(id)
  if (!styleTag) {
    styleTag = document.createElement('style')
    styleTag.setAttribute('id', id)
    document.head.appendChild(styleTag)
  }
  styleTag.innerText = newStyle
}